1. Field of the Invention
The present invention relates generally to cell-specific targeting peptides, to fusogenic peptides, to liposomes containing the cell-specific targeting peptides and/or fusogenic peptides, to methods of making the liposomes, and to therapeutic methods of using the liposomes to treat disorders.
2. Description of Related Art
For the past three decades, targeting drugs, oligonucleotides, and genes to a specific tissue have been one of the fundamental goals of the pharmaceutical industry. Until recently this has been a very elusive problem. One of the fundamental properties of living cells is their ability to sense and respond to their environment. This is accomplished by a specific set of receptors on the cell surface. Identifying the specific binding proteins and defining their specificity is a big stride towards resolving the problem of specific tissue targeting. The binding of targeting peptides to drugs raises many technical problems and in most cases affects the activity of the drug. The encapsulation of drugs in liposomes and other microcapsules give an important boost and opens new lines of research. Encapsulation can deliver a large number of drug molecules that are targeted towards a specific tissue, by protecting them from degradation by enzymes. Accomplishing this goal may reduce or even eliminate side effects by reducing the amount of drug needed and increasing its effectiveness due to its accumulation in the target tissue. Since most of the targeting peptides are water-soluble and the phospholipids are oil soluble, specific linkers and several steps are required for binding these two molecules. The situation gets more complicated when the conjugation of several peptides at different concentrations is required for the delivery of a gene.
Accordingly, it was an object of the present invention to provide a simplified means of incorporating targeting peptides into liposomes.
Another object was to identify new targeting peptides and their target cells.